I think that is so very important to provide a national Cycling proficiency.I had a couple of formal cycle training courses as a kid growing up. I forget precisely the order but can recall some details.
Firstly in the cubs, I did a full day's course on bike handling skills, rudimentary repair and maintenance, and a simulated road ride including obeying stop signs, how to indicate and so on. And also how to register your bike with the police using the frame number using a form you sent off in the post.
Secondly I did some kids' cycling proficiency courses (1 or 2 days) at Herne Hill Velodrome. It was my parents who put me on it - but I suspect this may have partly been funded by southwark council. But there were volunteers including my dad basically running the same content as the cub scouts course.
At this point I was doing the odd mountain bike ride and some velodrome cycling but no real commuting to school or road cycling. The real weakness of the above two courses was that they were taught either in a school playground or HHV, not on real roads.
Lastly, when a little older (around 15?) I did a day course about cycling on roads with confidence. This was actually pretty brilliant, I hadn't been confident cycling on roads until this point. In the course you learn things like adopting the primary position and put into practice what you've learned on real roads and lanes. I've been a confident road commuter ever since
Doing some research it seems to me that the modern equivalent of the last one is the 'cycle confident' scheme which is available throughout London - https://www.cycleconfident.com/sponsors/southwark/ . It looks a lot like what these 12 year old Dutch kids are doing to be honest, though they have the advantage of their fab bike infrastructure! Unfortunately where I live now doesn't seem to have anything like this on offer. And I'm not shocked to find out that 69% of local commutes which are less than 10km trips are done in a car...
Definitely worth doing in groups, families or alone IMO.